Warming beyond 1.5 would also "appreciably increase the prevalence of extreme storms that have already been capable of large-scale loss of life and cutting a year's GDP in half for some of our members."

At the last major conference of negotiators in Marrakech last November, members of the CVF committed themselves to moving towards 100% renewable energy as soon as possible.

"Costa Rica produces 100% renewable energy most of the year," said William Calvo, the country's adjunct chief negotiator.

"But we won't stop there: we are tackling now the transport sector and hope to even export renewable power more widely in the region."

The idea that other countries are capable of picking up the slack if the Americans pull out of Paris gained support this week with the release of an analysis showing that India and China are likely to overshoot existing targets to cut carbon.

Between 2013 and 2016 Chin's coal use declined each year and a continued slow decline is expected. India says that planned coal-fired power plants may not be needed if recently announced green policies are effective.

"You have to have the U.S. on board ultimately to meet the goals set by the Paris Agreement," Bill Hare from Climate Analytics told news agencies.

"But if there's a hiatus for four years it doesn't mean it's the end of the game."